Convection regimes and tropical midlatitude interactions over the Intra-American Seas from May to November

A cluster analysis is applied to National Oceanic and Atmospheric Administration daily outgoing longwave radiation anomaly fields over the Intra€American Seas, for the May to November rainy season 1980€“2009. Seven recurrent convection regimes are identified, each with distinct impacts on local rainfall. Three suppressed€convection regimes prevailing throughout the season and in particular during the Mid€Summer Drought are related to transient anticyclonic circulation anomalies and broad drying over the region. The remaining regimes are all related to enhanced convection and cyclonic circulation anomalies over the Caribbean. For one wet regime, the cyclonic anomaly is located over Central America, which increases moisture advection from the eastern Pacific and in turn rainfall over Central and South America to the disadvantage of northern regions of the Caribbean. The three other regimes are associated with a weaker Caribbean Low Level Jet along its southern branch stretching along the South American coast, while its northern branch is strengthened, exposing the Caribbean to more moisture advection from the northeast trade winds, enhancing convection and rainfall locally. These three wet regimes are related to northwestward€propagating convective cells that can be traced in a composite sense to the southward incursion of baroclinic waves from the midlatitudes, and anticyclonic wave breaking. In addition, their frequencies are found to be higher during phases 1 and 2 of the Madden€Julian Oscillation, suggesting a connection with easterly waves emanating from African convection. Relationships are shown between these three northwestward€propagating wet regimes and historical floods in the Caribbean illustrating the potential value of the convective regime approach for ultimately improving regional predictions and disaster early warning on sub€seasonal scales.